1. Field of the Invention
The present invention relates to an imaging apparatus having the function for reading an image in a magnified size. This function will be referred to as a "zooming" function, hereinafter.
2. Description of the Related Art
A known zooming method will be described with reference to FIGS. 9A to 9C. FIG. 9A is an illustration of an image formed on an imaging device, including a portion to be zoomed out, while FIGS. 9B and 9C are timing charts showing, respectively, the manner in which vertical scan is conducted during the operation of an imaging apparatus in a zoom-out reading mode and the manner in which the horizontal scan is conducted along horizontal lines which include the image portion to be zoomed out.
Referring to FIG. 9A, an image of an object is formed on a two-dimensional imaging device 101. It is assumed that only a portion 102 of the image is to be displayed on a greater scale, while the other portions of the image are to be neglected. To this end, it is necessary that the signals from the portion of the imaging device 101 corresponding to the image portion 102 are read in the effective television period, while signals from the other portions are read during the horizontal and vertical blanking periods.
Referring also to FIG. 9B, the signals from the scanning lines 1 to (a-1), corresponding to an unnecessary portion of the image, are shifted at a high speed in a period t.sub.1 within the vertical blanking period VBLK. The signals from the scanning lines a to b, covering the portion 102 of the image, are shifted at a low speed in a period t.sub.2 which is the vertical effective period. In this vertical effective period, each of the horizontal lines a to b is horizontally scanned in a manner shown in FIG. C.
Subsequently, the signals from the lowermost unnecessary portion, corresponding to scanning lines (b+1) to n, are shifted at a high speed in the next vertical blanking period t.sub.3.
The manner of the horizontal scan along each of the horizontal scanning lines a to b is conducted in a manner which will be explained hereinunder with reference to FIG. 9C. Namely, the signals from the unnecessary portion which is to the left of the image portion 102 to be zoomed out are shifted at a high speed in a period t.sub.21 within the first horizontal blanking period. Then, the signals from the portion corresponding to the image portion 102 are shifted at a low speed in the effective period t.sub.22. Finally, the signals corresponding to the unnecessary portion which is to the right of the image portion 102 are transferred at a high speed within the next horizontal blanking period t.sub.23.
In the described zoom-out reading operation, assuming that the magnification is 2, the image portion 102 includes n/2 horizontal scanning lines. If this image portion 102 is displayed with the magnification 2 on, for example, a television screen, therefore, the quality of the image is impaired due to the presence of noise in the form of horizontal stripes. In order to obviate this problem, known imaging apparatus usually employ memory means or delay means which store or delay the zoomed-out read signals such that the signal for each line is used twice, so as to provide n pieces of scanning lines on the display, thereby to avoid degradation of the quality of the display image.
This known imaging apparatus, however, requires a large and complicated circuit to perform this function and, hence, the production cost is raised due to the use of the memory or delay means which is intended for the multiple use described above of the image signals. The same problem is encountered also with an apparatus of the type which employs interpolation between a pair of distant line signals or prediction of a next line signal from the preceding line signal.
The circuit is further complicated when the signals are read through a plurality of signal lines.